Pineapple leaf fiber (PALF) has attracted increasing attention as an agricultural residue for the development of composite and functional materials. This review examines PALF from its composition and fundamental characteristics to its modification, processing, applications, and environmental implications. The chemical composition, morphology, crystallinity, thermal behaviour, and mechanical characteristics of PALF are discussed in relation to its performance in material systems. Particular attention is given to modification methods, including hot water, alkali, acid hydrolysis, bleaching, silane, calcium hydroxide, and combined treatments, and their effects on non-cellulosic constituents, fiber structure, and interfacial behaviour. The review further covers the fabrication of PALF-based composites using different polymer matrices and emerging applications involving aerogels and carbon-based materials. Available environmental evidence is also examined to identify the influence of fiber extraction and processing on carbon emissions and the potential environmental benefits associated with the utilization of agricultural residues and PALF biodegradability. By bringing these aspects together, this review provides an updated assessment of the factors governing the processing and performance of PALF-based materials and identifies areas requiring further investigation.